Most of the cytostatics in use today either inhibit the formation of essential precursors for biosynthesis of DNA or block DNA polymerases or interfere with the template function of DNA because DNA was the primary target for developing therapeutic drugs for chemotherapy. Unfortunately, inhibition of the formation of essential precursors for biosynthesis of DNA or blocking DNA polymerases or interference with the template function of DNA also affects normal tissues.
Antimicrotubule drugs are a major category of anticancer agents (Rowinsky, E. K., and Tolcher, A. W. Antimicrotubule agents. In: V. T. Devita, Jr., S. Hellman, and S. A. Rosenberg (eds.), Cancer Principles and Practice, Ed. 6, pp. 431-452. Philadelphia: Lippincott Williams and Wilkins, 2001). They work by interfering with the function of cellular microtubules, particularly the mitotic spindle. The disruption of normal spindle function leads to apoptotic cell death.
Currently, there are three major classes of known antimicrotubule pharmacological agents. Each has a distinct binding region on β-tubulin and distinct effects on microtubule function. These classes are: 1) taxane-site agents which promote microtubule formation and stabilize microtubules; 2) vinca/peptide-site agents which destabilize microtubules and often induce formation of abnormal polymers or aggregates at high concentrations; and 3) colchicine-site agents which also destabilize microtubules and generally do not induce other polymers (Hamel, E. Antimitotic natural products and their interactions with tubulin. Med. Res. Rev., 16: 207-231,1996). Most of the ligands for all three classes of sites are natural products or semi-synthetic derivatives of natural products.
Paclitaxel and its semisynthetic derivative docetaxel (Taxotere®) interfere with microtubule formation and stabilize microtubules. Paclitaxel (Taxol®), is a diterpene isolated from the bark of the Western (Pacific) yew, Taxus brevifolia and is representative of a new class of therapeutic agent having a taxane ring system. It was additionally found in other members of the Taxacae family including the yew of Canada (Taxus canadensis) found in Gaspesia, eastern Canada and Taxus baccata found in Europe whose needles contain paclitaxel and analogs and hence provide a renewable source of paclitaxel and derivatives. The crude extract was tested for the first time during the 1960s and its active principle was isolated in 1971 and the chemical structure identified (M. C. Wani et al, J. Am. Chem. Soc., 93, 2325 (1971)). Further, a wide range of activity over melanoma cells, leukemia, various carcinomas, sarcomas and non-Hodgkin lymphomas as well as a number of solid tumors in animals was shown through additional testing. Paclitaxel and its analogs have been produced by partial synthesis from 10-deacetylbaccatin III, a precursor obtained from yew needles and twigs, and by total synthesis (Holton, et al., J. Am. Chem. Soc. 116:1597-1601 (1994) and Nicolaou, et al., Nature 367:630-634 (1994)). Paclitaxel has been demonstrated to possess antineoplastic activity. More recently, it was shown that the antitumor activity of paclitaxel is due to a promotion of microtubule polymerization (Kumar, N., J. Biol. Chem. 256:10435-10441 (1981); Rowinsky, et al., J. Natl. Cancer Inst., 82:1247-1259 (1990); and Schiff, et al., Nature, 277:665-667 (1979)). Paclitaxel has now demonstrated efficacy in several human tumors in clinical trials (McGuire, et al., Ann. Int. Med., 111:273-279 (1989); Holmes, et al., J. Natl. Cancer Inst., 83:1797-1805 (1991); Kohn et al., J. Natl. Cancer Inst., 86:18-24 (1994); and A. Bicker et al., Anti-Cancer Drugs, 4,141-148 (1993).
Two taxane-site agents (paclitaxel and docetaxel) and three vinca/peptide-site agents (vinblastine, vincristine, and vinorelbine) are used clinically to treat various human cancers. Taxanes have proven to be of greater utility against solid tumors (e.g., lung, breast, ovarian) than the vinca alkaloids, suggesting that agents that promote microtubule formation might be superior clinically to those that destabilize microtubules. Colchicine-site agents are not used therapeutically.
Despite the widespread clinical use of paclitaxel and docetaxel, these drugs have several limitations that create a need for improved agents. First, many tumors are inherently resistant (e.g., colon tumors) or become resistant after multiple cycles of treatment, at least in part due to the expression of drug transporters located in cancer cell membranes that pump the drugs out of cells and thereby decrease their efficacy (Gottesman, M. M. Mechanisms of cancer drug resistance. Annu. Rev. Med., 53: 615-627, 2002). The best known of these transporters is P-glycoprotein. Accordingly, there is a need for new agents with taxane-like effects on microtubule polymerization that are not substrates of P-glycoprotein or other such pumps and that therefore will overcome this cause of taxane resistance in patients.
Second, paclitaxel and docetaxel have poor water solubility and paclitaxel must be formulated in Cremophor EL, a vehicle that induces serious hypersensitivity reactions (Li, C. L., Newman, R. A., and Wallace, S. Reformulating paclitaxel. Science & Medicine, January/February: 38-47,1999). Patients are typically premedicated with corticosteroids and antihistamines before administration of paclitaxel to minimize these toxicities. Accordingly, there is a need for new agents with taxane-like effects on microtubule polymerization that are highly water soluble and can be administered in physiological saline or other suitable non-toxic vehicle.
Third, paclitaxel is a natural product having a highly complex structure, and docetaxel is a closely related semisynthetic derivative. Therefore there is a need for compounds which are readily available through synthesis, are structurally different from taxanes and which have taxane-like effects on microtubule polymerization.
Accordingly, there is still a need in the art for cytotoxic agents for use in cancer therapy. In particular, there is a need for cytotoxic agents which inhibit or treat the growth of tumors which have an effect similar to paclitaxel and interfere with the process of microtubule formation. Additionally, there is a need in the art for agents which accelerate tubulin polymerization and stabilize the assembled microtubules.
Further, it would be advantageous to provide new compounds which provide a method of treating or inhibiting cell proliferation, neoplastic growth and malignant tumor growth in mammals by administering compounds which have paclitaxel like anticancer activity.
Additionally, it would be advantageous to provide new compounds which provide a method for treating or inhibiting growth of cancerous tumors that express multiple drug resistance (MDR) or are resistant because of MDR.
Further, it would be advantageous to provide new compounds which provide a method of treating or inhibiting the growth of cancerous tumors in a mammal with inherent or acquired resistance to chemotherapeutic agents and in particular antimitotic agents.
Described in the art is the preparation and use of substituted triazolopyrimidines in agriculture as fungicides and are disclosed in U.S. Pat. Nos. 5,593,996; 5,756,509; 5,948,783; 5,981,534; 5,612,345; 5,994,360; 6,020,338; 5,985,883; 5,854,252; 5,808,066; 5,817,663; 5,955,252; 5,965,561; 5,986,135; 5,750,766; 6,117,865; 6,117,876; 6,124,301; 6,204,269; 6,255,309; 6,268,371; 6,277,856; 6,284,762; 6,297,251; 6,387,848; US Patent Application Publication US2002/0045631A1; US2002/0061882A1; US20030055069A1 and International Publication Numbers: WO98/46607; WO98/46608; WO99/48893; WO99/41255; WO00/18227; WO01/35738A2; WO02/46195A1; WO02/067679A1; WO02/083676A1; EPO 834513A2; EPO 782997A2; EPO550113B1; FR2784381A1; EPO 989130A1; WO98/41496; WO94/20501; EPO 945453A1; EPO 562615A1; EPO 562615B1; EP 0 550113A2; EP 0 943241B1; EP 0 988790 B1 and having the following general formula:

Also known are the use of triazolopyrimidines as anticancer agents having the structural formula
described in WO02/02563 A2.
5,7-Dihydroxyimidazo[1,2-a]pyrimidine without phenyl substitution at the 6-position is known (R. P. Rao et al, J. Het. Chem. 1021 (1973)). Also known is 5,7-dichloroimidazo[1,2-a]pyrimidine without phenyl substitution at the 6-position (G. R. Revankar, et al, J. Med. Chem. 18, 1253 (1975)).
EP 0,770,615 provides a process for the synthesis of dihaloazolopyrimidines of the formula
wherein:    X, is chlorine or bromine;    R is optionally substituted phenyl;    X, Y, and Z are CR1 or N and further described is the synthesis of 5,7-dihydroxy-6-(2-chloro-6-fluorophenyl)benzimidazopyridine having the structural formula

Described in JP2001043978 are diazaindolizines represented by the generic structure
wherein said compounds are useful as electroluminescent elements.
Described in WO 03/022850 A1 are imidazo[1,2-a]pyrimidines represented by the following general formula
wherein said compounds are useful as fungicides.
The compounds of this invention are a new class of taxane-like agents that satisfy the hereinbefore described needs, and that differ in significant ways from the previously known classes of antimicrotubule compounds. The compounds of this invention bind at the vinca site of β-tubulin, yet they have many properties that are similar to taxanes and distinct from vinca-site agents. In particular, the compounds of this invention enhance the polymerization of microtubule-associated protein (MAP)-rich tubulin in the presence of GTP at low compound:tubulin molar ratios, in a manner similar to paclitaxel and docetaxel. Representative examples of the compounds of this invention also induce polymerization of highly purified tubulin in the absence of GTP under suitable experimental conditions, an activity that is a hallmark of taxanes. The compounds of this invention are potently cytotoxic for many human cancer cell lines in culture, including lines that overexpress the membrane transporters MDR (P-glycoprotein), MRP, and MXR, thus making them active against cell lines that are resistant to paclitaxel and vincristine.